Since the update, Bad hint flags don’t stick.
I have just tried to reproduce this and I wasn’t able. It seems that flagging of bad hints works fine for me. Which browser are you using? When you click on flag, yellow sign with exclamation should appear and it should be there every time when you are over that bad hint with your mouse pointer.
It appears to work fine but in essence, when you go back to a lingQ that you have previously flagged, the flag is no longer there. This differs from the way it worked before the last update. I’m using Chrome.